Aromatic bis(ether phthalimide) compounds are known intermediates used in the synthesis of certain polyimides. These compounds are readily converted to the corresponding aromatic bis(ether anhydride) compounds by known methods. One example of such methods involves hydrolysis of the aromatic bis(ether phthalimide) with aqueous sodium hydroxide to produce a tetracarboxylic acid salt which is thereafter acidified to the tetracarboxylic acid, followed by dehydration of the tetracarboxylic acid to produce the aromatic bis(ether anhydride). (See U.S. Pat. No. 3,879,428.) A similar method is disclosed in U.S. Pat. No. 3,933,852, in which certain bis(N-methyl phthalimide)ethers are treated with aqueous sodium hydroxide and water to form the corresponding tetracarboxylic acid, which then is treated with, for example, glacial acetic acid and acetic anhydride to obtain the corresponding dianhydride.
The thus-derived aromatic bis(phthalic dianhydride)ethers are useful as monomers for the preparation of various polyimide homopolymers and copolymers. See, for example, Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Ed., John Wiley and Sons, Inc., New York (1971), Supplemental Volume, pp. 746-755. U.S. Pat. No. 3,847,867 describes the production of polyetherimides by reacting certain aromatic bis(ether anhydrides) with organic diamines.